The invention relates to a latch needle for a loop-forming machine, in particular for a knitting machine, for the production of flat textiles.
In order to form loops of a minimum of one thread, so-called latch needles are used in machines, in particular knitting machines, whereby, in operative mode, said needles are moved back and forth in rapid succession. In so doing, the latch provided on such a latch needle opens and closes a receiving space in rapid succession and at high speed. When the latch changes from closed position into the rear position, the latch head performs an oscillating movement in the form of an arc of a circle. In so doing, the latch alternately impacts on the hook in rapid succession in order to create the closed position, as well as on the shaft of the latch needle, in order to create the open position or rear position.
The thread-receiving space is limited by a needle base body and its hook on one end while interacting with the opening and closing latch. If so-called small-grooved latch needles are used, the tip of the hook sinks into a depression in the noucat at the end of the latch. By receiving the hook tip in the depression of the latch head, it is ensured that the hook tip is almost fully covered by the latch head. This facilitates casting off the half-loops via the latch head and thus facilitates the loop formation. During the casting-off process, the half-loop slides from the upper side of the needle over the latch shaft and subsequently over the latch head. The relatively wide latch head facilitates the interaction of the latch head and the hook, in that the latch head reliably impacts on the hook, even in cases of greater latch bearing tolerances.
The latch needles are held in a needle carrier so that they can be moved back and forth, in which case said needles are moved back and forth in longitudinal direction—controlled by cams—in order to form loops. In order to ensure the rapid back and forth movement, the shaft width of a latch needle is slightly smaller than the width of a needle channel associated with said needle. Based on the existing manufacturing tolerance of the needle channels and the needle shaft width, it is possible that a latch needle—affected by the rotation of the needle carrier of a circular knitting machine—is inclined with respect to the center axis of a guide channel.
Referring to a circular knitting machine, sometimes up to 6,000 knitting machine needles are arranged at a small distance from each other. In addition, between each two needles there is respectively one sinker that is required for the loop-forming process. On the one hand, this sinker aids the so-called casting-off of the loops over the closed latch and, on the other hand, it holds down the knit product.
As a result of the tolerances existing in the guide channel of the needle bed and the tolerances in the region of the latch bearing, the knitting machine needle and its latch are respectively displaced with respect to their ideal position. These tolerances increase because of the wear during prolonged use of the knitting machine needle, thus also causing the lateral displacement of the latch to be increased. Referring to knitting machines, which have little intermediate space for the passage of the latch between the needles and the sinkers during the oscillating movement, contact may occur between the latch head and a sinker adjacent to said head. In so doing, the sinker, as well as the latch head are worn, which is disadvantageous.
In order to avoid this, so-called male latch-female hook type latch needles have been suggested. In so doing, document DE OS 28 34 558 discloses a knitting machine needle having a hook, which, in the region of the tip has a relatively deep depression. This depression receives part of the latch spoon, whereby said depression is limited by two lateral surfaces arranged at an acute angle with respect to each other, said lateral surfaces partially extending beyond the latch spoon when the latch is in closed position. The width of the latch is smaller than the width of the hook and thus substantially smaller than the width of the needle shaft. However, the result of this is that, during the casting-off process, the half-loop drags on the part of the hook tip that is not covered by the latch head and, in the worst case, is caught, thus interrupting the casting-off process. This, in turn, negatively affects the loop formation.
Another disadvantage of a male latch-female hook type needle is that the relatively narrow latch head tends to laterally slide on the hook past the inside space of the hook. This risk increases with increasing wear of the latch bearing.
A further disadvantage of a male latch-female hook type needle is that the transition from the latch shaft inside to the hook tip is not stepless when the latch is in closed position. This increases the risk that, in particular when plating, i.e., knitting with two threads, one of these two threads escapes between the closed latch and the hook. As a result, defective goods are produced.
Document DE 100 57 765 discloses one way of solving this problem. To achieve this, it is suggested to provide, on the latch shaft inside, a projection so that a stepless transition from the latch shaft inside into the hook inside space becomes possible. This solution is used in many cases, whereby the increased size of the latch due to the projection has been found to be disadvantageous, in particular in knitting machines.
Likewise, U.S. Pat. Nos. 2,282,824 and 773,722 disclose male latch-female hook type knitting machine needles that exhibit the aforementioned disadvantages.